A stabilizer is a ball joint part connecting an arm or a strut of a suspension apparatus and a stabilizer apparatus. FIG. 1 is a perspective view showing a schematic structure of a front side wheel of a vehicle. Each suspension apparatus 1 is provided at left and right tires 4 and has an arm 11 and a cylinder 12. A lower end portion of the arm 11 is fixed at a bearing supporting a shaft of the tire 4. The cylinder 12 is elastically movable relatively to the arm 11. A bracket 13, to which a stabilizer link 3 is mounted, is provided at the arm 11. The suspension apparatus 1 supports the weight of a vehicle body that is applied to the tire 4. A stabilizer apparatus 2 is equipped with a bar 21 that is approximately U-shaped, and the stabilizer apparatus 2 is mounted to the vehicle body via bushes 22. The stabilizer apparatus 2 secures rolling stiffness of the vehicle.
The stabilizer links 3 are provided at the bracket 13 of the suspension apparatus 1 and at the end portion of the bar 21 of the stabilizer apparatus 2. The stabilizer links 3 are connected to each other by a support bar 70. The stabilizer link 3 transmits a load, which is generated when the suspension apparatus 1 receives an input from a road surface, to the stabilizer apparatus 2.
FIG. 2 is a side sectional diagram showing a portion of a structure of a specific example of the stabilizer link 3. The stabilizer link 3 is equipped with a ball stud 30, a ball seat 40, a housing 50, and a dust cover 60.
The ball stud 30 has a stud portion 31 and a ball portion 32 which are integrally formed. The stud portion 31 has a tapered portion 33, a straight portion 34, and a screw portion 35. The tapered portion 33 is formed at an upper end portion of the ball portion 32. A collar portion 36 and a projection portion 37 are formed at an upper end portion and a lower end portion of the straight portion 34. An upper end portion 61 of the dust cover 60 abuts between the collar portion 36 and the projection portion 37 at the straight portion 34 so as to be fixed therebetween. The screw portion 35 of the stabilizer link 3 proximate to the suspension apparatus 1 is fixed at the bracket 13 of the arm 11 by screw fastening, and the screw portion 35 of the stabilizer link 3 proximate to the stabilizer apparatus 2 is fixed at the bar 21 by screw fastening.
The ball seat 40 and the housing 50 form a pivot support member that universally supports the ball stud 30. The ball portion 32 of the ball stud 30 is press-fitted into the ball seat 40. The housing 50 holds the ball seat 40 therein. A lower end portion 62 of the dust cover 60 is held between flange portions 41 and 51 of the ball seat 40 and the housing 50.
Thermal caulking portions 42 are formed at a bottom portion of the ball seat 40 by a thermal caulking method. Specifically, the thermal caulking portion 42 is a resin portion formed by heating and transforming a pin portion of the ball sheet 40 using a heat caulking apparatus. Each thermal caulking portion 42 projects through a hole 52 of a bottom portion of the housing 50, and a leading end portion of the thermal caulking portion 42 engages with a lower surface portion of the housing 50. The ball seat 40 is fixed at the housing 50 by the thermal caulking portion 42 (for example, Patent Document 1).
However, in the heat caulking method, a heat caulking portion 42 made of resin is exposed to the outside, and therefore, there is a problem in that the thermal caulking portion 42 is broken by adhering strong acid or by contacting a foreign substance. Moreover, there is a problem in that the stud releasing load is not drastically improved, since formation position of the heat caulking portion 42, etc., is seriously constrained.
Therefore, in order to solve the above problem due to the heat caulking method, a method (a housing caulking method) in which a caulking portion at an upper end portion of the housing is caulked toward an upper end portion of the ball sheet and an upper end portion of the ball sheet is pressed and fixed by the caulking portion, is proposed, instead of the heat caulking method.
However, in the housing caulking method, since an opening side of the ball sheet is directly fixed by the caulking portion of the housing, load (caulking load) applied by the caulking portion directly acts to the opening side of the ball sheet. Therefore, the ball sheet is excessively pressed, and a positional relationship between the ball sheet and the ball stud is not appropriately ensured, and frictional force therebetween is unstable. As a result, there is a problem in that torque characteristics, etc., are unstable.
Therefore, the applicants has proposed a structure in which a ring member is interposed between a caulking portion of a housing and an opening side of a ball sheet (for example, Patent Document 2). The ring member has a stopper base portion or a stopper taper portion. The stopper taper portion is formed at an inner peripheral side of the stopper base portion and is inclined, so that diameter thereof is decreased from the opening side toward an axial direction of the stopper base portion.
In the housing caulking method using such ring member, the stopper base portion is abutted to an opening end surface of the ball sheet, the stopper taper portion is abutted to a slope portion for a stopper taper of the ball sheet, and the caulking portion of the housing is caulked inwardly. Thus, the opening side of the ball sheet can be pressed through the ring member by the caulking portion of the housing.
Patent Document 1 is Japanese Unexamined Patent Application Publication No. Hei 6-117429, and Patent Document 2 is Japanese Unexamined Patent Application Publication No. 2010-156466.